Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$154.34	9.241%	$168.6026	$168.60	$168.60	$168.60
Purchase #2	$187.85	11.589%	$209.6199	$209.62	$209.60	$209.60
Purchase #3	$116.69	13.520%	$132.4665	$132.47	$132.45	$132.50
Purchase #4	$146.31	12.775%	$165.0011	$165.00	$165.00	$165.00
Purchase #5	$47.64	13.535%	$54.0881	$54.09	$54.10	$54.10
Purchase #6	$138.72	10.123%	$152.7626	$152.76	$152.75	$152.80
Purchase #7	$117.56	9.810%	$129.0926	$129.09	$129.10	$129.10
7 purchase totals =	$909.11		$1,011.6334	$1,011.63	$1,011.60	$1,011.70